An IN738 alloy with a high Al and Ti contents induces a significant cracking tendency during laser powder bed fusion (LPBF) processing, leading to a mismatch between printability and mechanical properties. Modification of alloy compositions is an effective strategy to enhance the printability and mechanical properties of nickel-based superalloys via LPBF. In this study, the effects of adding 5 wt.%Co on the printability and mechanical properties of LPBF-fabricated IN738 were investigated by using three-dimensional high-resolution micro-computed tomography (micro-CT), electron backscatter diffraction (EBSD), and quasi-static room-temperature tensile tests. The results show that adding 5 wt.%Co can significantly reduce the defect rate and defect size of the LPBF-fabricated IN738 alloy, remarkably improve alloy densification, and optimize printability. Meanwhile, compared with the LPBF-fabricated IN738 alloy, the 5 wt.%Co-IN738 alloy exhibits an excellent balance of strength and ductility in horizontal and vertical directions, both LPBF-fabricated and heat-treated. These results are anticipated to offer valuable guidance for the development of LPBF-fabricated Ni-based superalloys that achieve a favorable balance between printability and mechanical properties.

In this paper, solution-treated Inconel 625 alloy was selected as the research object. Combined with the low-energy characteristic of annealing twin boundaries and the synergistic strengthening effect of gradient structures, the alloy microstructure was tailored without altering its chemical composition. The evolution mechanism of grain size and twin boundary fraction, as well as their influence on corrosion resistance, were investigated. On this basis, the synergistic strengthening effect of gradient structure and interface regulation on the corrosion and mechanical performance of the alloy was further explored. The results show that a gradient-structured Inconel 625 alloy with abundant annealing twins and high-density grain boundaries can be fabricated by surface nanocrystallization combined with high-temperature short-time annealing. The variation in annealing twin fraction with grain size in interface-modified Inconel 625 complies with the Pande model. In terms of corrosion resistance, the microstructure consisting of fine grains and a high fraction of annealing twins exhibits superior performance compared to coarse grains with identical twin content. Its corrosion potential is tripled, while the corrosion current density is reduced by 11 times, delivering outstanding anti-corrosion capability in NaCl solution. Benefiting from the integrated merits of gradient architecture, annealing twins and fine grains, the interface-tailored Inconel 625 alloy achieves excellent comprehensive performance, with a yield strength of 925 MPa, elongation of 26%, and corrosion current density of 3.02 × 10⁻⁸ A/cm², realizing the integration of high strength, good ductility and superior corrosion resistance for Inconel 625 alloy.